Diurnal changes in net photosynthetic rate (PN), chlorophyll (Chl) fluorescence, and stomatal aperture of several hybrid poplar clones subjected to midday light stress were measured in July and August of 1996. Midday depression of PN, photosystem 2 (PS2) efficiency, stomatal conductance (gs), and stomatal aperture was observed in all clones, though at differing rates among them. Non-uniform stomatal closure occurred at noon and at other times, requiring a modification of intercellular CO2 concentration (C1). A linear relationship was found between gs and stomatal aperture. More than half of the photons absorbed by PS2 centre dissipated thermally when subjected to light stress at noon. There was a linear relationship between the rate of PS2 photochemical electron transport (PxPFD) and PN. There was a consensus for two fluorescence indicators (1 - qP/qN and (Fm' - F)/Fm') in assessment of susceptibility of photoinhibition in the clones. According to PN, Chl fluorescence, and stomatal aperture, we conclude that midday depression of photosynthesis can be attributed to both stomatal and non-stomatal limitations. and Shouren Zhang, Rongfu Gao.
The photochemical activity of native Central Siberian Scots pine trees (Pinus sylvestris L) was estimated from the middle of February to the middle of March 2001. We measured chlorophyll (Chl) fluorescence in attached intact needles from trees located approx. 30 km west of the Yenisey river (60°44'N, 89°09'E) near the village of Zotino. In this period, the air temperature varied between -39 °C and +7 °C. At temperatures below -10 °C, P. sylvestris needles did not exhibit any variable Chl fluorescence during the daylight period. During the night, however, the effective quantum yield of photosystem 2 (PS2) photochemistry, Φ2 [Φ2 = (Fm' - Ft)/Fm'), increased from values near zero to values between 0.05 and 0.20 depending on the needle temperature and sample investigated. The increase started soon after dusk and lasted for 3-6 h depending on the temperature. A faster increase of Φ2 was found for temperatures around -16 °C, and lower rates occurred at lower temperatures. Irrespective of the temperature, Φ2 decreased rapidly to near zero values at dawn, when the photosynthetic photon flux density increased to about 1-5 µmol m-2 s-1, and remained near zero throughout the day. At temperatures higher than -10 °C, the diurnal decrease and the nocturnal increase of Φ2 were less distinct or disappeared completely. Hence the winter-adapted Scots pine maintains some photochemical activity of PS2 even at extremely cold temperatures. The capacity of photochemical reactions below -10 °C is, however, very limited and PS2 photochemistry is saturated by an extremely low irradiance (less than 5 µmol m-2 s-1). and P. Šiffel, J. Šantrůček.
Chlorophyll (Chl) fluorescence of warm day/cool night temperature exposed Phalaenopsis plants was measured hourly during 48 h to study the simultaneous temperature and irradiance response of the photosynthetic physiology. The daily pattern of fluorescence kinetics showed abrupt changes of photochemical quenching (qP), non-photochemical quenching (NPQ) and quantum yield of photosystem II electron transport (ΦPSII) upon transition from day to night and vice versa. During the day, the course of ΦPSII and NPQ was related to the air temperature pattern, while maximum quantum efficiency of PSII photochemistry (Fv/Fm) revealed a rather light dependent response. Information on these daily dynamics in fluorescence kinetics is important with respect to meaningful data collection and interpretation. and B. Pollet ... [et al.].
In field-grown Cyamopsis seedlings, distinct changes were found in the rates of photosystems (PS) 2 and 1 activities at different time of the day. Maximum PS2 activity was at around 11:00 h and decreased thereafter. On the contrary, PS1 activity continued to increase up to 14:00 h and declined in evening hours. Significant energy transfer from PS2 to PS1 was evident during the morning and evening hours of the day whereas a slow excitation of PS2 and energy transfer was favoured during noon hours. and K. Lingakumar, G. Kulandaivelu.
Net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), leaf water potential (ψleaf), leaf nitrogen content, and photosynthetic nitrogen use efficiency (PNUE) were compared between a typical C4 plant, Agriophyllum squarrosum and a C3 plant, Leymus chinensis, in Hunshandak Sandland, China. The plant species showed different diurnal gas exchange patterns on June 12-14 when photosynthetic photon flux density (PPFD), air temperature (Tair), and water potential were moderate. PN, E, and
gs of A. squarrosum showed distinct single peak while those of L. chinensis were depressed at noon and had two peaks in their diurnal courses. Gas exchange traits of both species showed midday depression under higher photosynthetic photon flux density (PPFD) and T air when Ψleaf was significantly low down on August 6-8. However, those of A. squarrosum were depressed less seriously. Moreover, A. squarrosum had higher PN, Ψleaf, water use efficiency (WUE), and PNUE than L. chinensis. Thus A. squarrosum was much more tolerant to heat and high irradiance and could utilise the resources on sand area more efficiently than L. chinensis. Hence species like A. squarrosum may be introduced and protected to reconstruct the degraded sand dunes because of their higher tolerance to stress and higher resource use efficiency. and S. L. Niu ... [et al.].
Yields of wheat in semiarid and arid zones are limited by drought, and water condition is very important at each stage of development. Studies carried out at Loess Plateau in the northwestern part of China indicated that yield of spring wheat (Triticum aestivum L.) cv. Dingxi 81-392 was reduced by 41% when subjected to water stress. The effects of two water regimes on net photosynthetic rate (PN), stomatal conductance (gs), and intercellular CO2 concentration (Ci) were investigated at the jointing, booting, anthesis, and grain filling stages. Low soil moisture in comparison to adequate one had invariably reduced PN during the diurnal variations at the four growth stages. PN and gs in both soil moisture regimes was maximally reduced at midday. Ci and the stomatal limitation fluctuated remarkably during photosynthesis midday depression processes, especially at the grain filling stage. Hence atmospheric drought at midday was one of the direct causes inducing stomata closure and the gs depression, but it was beneficial for maintaining stable intrinsic water use efficiency. Fluctuation in Ci implicated that non-stomatal limitation also plays an important role during the period of photosynthesis midday depression. Consequently stomatal and/or non-stomatal limitation are the possible cause of the midday photosynthesis decline. and Xi-ping Deng ... [et al.].
We analyzed the eddy covariance measurements of momentum, mass, and energy taken daily throughout five consecutive seasonal courses (i.e. 840 d after planting) of a pineapple [Ananas comosus (L.) Merr. cv. Red Spanish] field growing in the Orinoco lowlands. This field provides an opportunity for micrometeorological studies because of the flat and windy site; the seasonal weather including ENSO effects and the Crassulacean Acid Metabolism (CAM) physiology of the crop were additional attributes. Soil CO2 flux was quantified and added to the net ecosystem exchange in order to obtain the canopy flux (FC). The canopy CO2 flux partially followed the four phases of CAM sensu Osmond (1978). The daily pattern of gaseous exchange in pineapple showed a continuum spectrum in which a major proportion of CO2 uptake occurring during the daytime was common and in which the CAM expression was related to day and nocturnal CO2 uptake. However, the benefits of CO2 uptake at low water cost were constrained by the limited nocturnal CO2 uptake. Seasonal and ontogenetic changes affected the energy exchange as well as the partitioning of available energy into sensible (QH) and latent (QLE) heat. When the hourly net radiation (QRn) reached its maximum value, latent heat flux (QLE) to available energy throughout the vegetative and reproductive stages was 0.65, 0.05, 0.30, 0.11, and 0.33 for the 1997 wet season, 1997/98 dry season, 1998 wet season, 1998/99 dry season, and 1999 wet season, respectively. Throughout the growth period, we found the pivotal role of surface conductance (gs) in both QLE and FC. Furthermore, the canopy responded to environmental changes. During the wet seasons the gs was strongly influenced by humidity mole fraction deficit and was usually lower than aerodynamic conductance, whereas during the dry seasons, soil water deficit limited evapotranspiration and production rates. For the fully canopy cover, the hourly trend of marginal water cost of pineapple carbon gain in the dry seasons indicated that gs became sufficiently efficient to reduce the amount of water transported per unit of carbon gain. In the wet season, the coupling of CO2 uptake and stomatal conductance was more effective in maintaining a higher proportionality between QLE and gs. and J. San-José, R. Montes, N. Nikonova.
Diurnal changes of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity and its content were measured to find the mechanism of RuBPCO activity regulation in Norway spruce needles. Both initial and total RuBPCO activities as well as the activation state had a typical pattern with two peaks in the morning and afternoon, respectively, and a midday depression. On the 19 October, RuBPCO content decreased during the day from 3.1 to 1.4 g m-2, while on the 20 October it was approximately constant both in the morning and in the afternoon (2.7 g m-2). Neither initial nor total activity of RuBPCO copied irradiances. Relatively low morning and evening values of total activities indicate that nocturnal inhibitor CA1P is important in Norway spruce. However, the midday depression of total activity indicates that besides CA1P there function some other inhibitors of RuBPCO. In addition, the diminution of RuBPCO content during the day may indicate repression of its gene expression. and M. Hrstka ... [et al.].
The effects of the diurnal variations in ambient temperature on some C3 and C4 enzymes in the Salsola dendroides and Suaeda altissima species of Chenopodiaceae family were studied during the intensive vegetation period. Activities of phosphoenolpyruvate carboxylase (PEPC) and cytosolic aspartate aminotransferase (AsAT) were shown to decrease in both species in the afternoon and evening. The activity of the mitochondrial AsAT decreased in S. altissima, remained relatively constant in S. dendroides during the day. The activity of alanine aminotransferase was high in the S. dendroides species in the morning and evening and decreased in the S. altissima species by the evening. Glucose-6-phosphate activated PEPC in both species throughout the day. The study of the redox status-regulated C3 enzymes showed temperature-related increases in NADP-glyceraldehyde 3-phosphate dehydrogenase activity in both plants, in fructose-2,6-bisphosphatase activity in the S. altissima species, and in NADP-MDH activity in the S. dendroides species in the afternoon., T. Y. Orujova, S. M. Bayramov, U. A. Gurbanova, H. G. Babayev, M. N. Aliyeva, N. M. Guliyev, Y. M. Feyziyev., and Obsahuje bibliografii
The 24-hour urinary excretion of 6-β-hydroxycortisol (6β-OHC) and the urinary ratio of 6β-hydroxycortisol/cortisol (6β-OHC/UFC) have been proposed as noninvasive probes for human cytochrome P450 3A4 isoform (CYP3A4). In this study, we evaluated within- and between-day variability of 6β-OHC excretion and 6β-OHC/UFC ratio in nine Caucasian men with cardiac disease. Each study participant was asked to collect 24-hour urine specimens during four consecutive days in five standardized time intervals. Concentrations of UFC and 6β-OHC were determined by immunoassay and the high-performance liquid chromatographic (HPLC) method, respectively. The HPLC method was accurate and precise, as indicated by the recovery rate of 96.5-103.3 % and less than 5.2 % and 6.3 % of the coefficient of variation for within-run and between-run assay, respectively. In patients, diurnal variations in UFC and 6β-OHC excretion were parallel. Consequently, 6β-OHC/UFC ratio remained stable during the day. Both, 6β-OHC excretion and 6β-OHC/UFC ratio showed significant relationship between 24-hour value and values measured in corresponding collection periods with best correlations obtained from night interval (22.00-06.00, r = 0.86-0.91). These results indicated that urinary 6β-OHC excretion and 6β-OHC/UFC ratio measured in overnight/morning urine could precisely reflect 24-hour values even in severely ill patients. In addition, a simple and sensitive HPLC method was described for determination of 6β-OHC in urine., S. Mičuda, L. Šišpera, M. Hodač, P. Pařízek, L. Fuksa, E. Brčáková, J. Cerman, J. Cermanová, J. Martínková., and Obsahuje bibliografii a bibliografické odkazy